1. Field of the Invention
This invention relates to the field of inspection, particularly to ultrasonic inspection of metal parts.
2. Description of the Prior Art
Conventional ultrasonic inspection equipment and methods utilize piezoelectric crystals for injecting a narrow beam of elastic waves into the part being inspected. Such transducers do not lend themselves to rapid inspection of high production parts because they must be moved along the surface of the part in tight contact with the part. In some cases, water can be used as a medium for conducting waves from the transducer into the part. However, such technique is still not suitable for the complete inspection of cylindrical objects under high speed conditions.
More recently, non-contact electromagnetic transducers (commonly called EMAT's) have been developed which utilize the interaction between a static magnetic field and an induced eddy current in the material being inspected to create dynamic forces in the material. On such electromagnetic transducer is the meander coil transducer described in U.S. Pat. No. 3,850,028.
EMAT's can be used in a manner similar to the earlier developed piezoelectric transducer by placing the transducer against a stationary part. However, a need exists for more rapid automatic inspection of parts, particularly for the inspection of high production parts such as artillery shells, vehicle parts, and other mass produced items. Until the present invention, EMAT's have not found extensive use for inspection of mass produced parts, because apparatus and methods taking advantage of their special features have not been available.